This invention relates to a liquid dispensing and vapor recovery system and, more particularly, to such a system in which liquid is dispensed from a storage tank to a receptacle while vapors from the receptacle are drawn to the storage tank.
With the increased emphasis on preventing pollution of the atmosphere, recent attention has been directed to minimizing the introduction of gasoline vapors into the atmosphere from both permanent type underground storage tanks for the gasoline, and from the vehicles into which the gasoline is ultimately dispensed.
Gasoline vapors can easily be recovered from underground storage tanks by providing a separate vapor return line which connects the storage tank to the transport truck which periodically fills the tank. In this manner, the gasoline introduced into the tank from the transport truck will displace the vapors and force them through the vapor recovery line to the truck whereby they are ultimately disposed of either by burning or through compression - refrigeration systems.
However, it has been extremely difficult to devise a satisfactory vapor recovery system from the gasoline tanks of vehicles. For example, previous proposals have utilized what is commonly referred to as a balanced displacement system in which the gasoline entering the tank forces the vapors through a separate line to the storage tank. However, this system has been less than satisfactory for several reasons, one of which is the difficulty in creating a proper seal between the gasoline dispensing and recovery nozzle and the automobile tank.
Although it has also been suggested to use a vacuum pump or a blower to remove the vapors from the vehicle tanks, this type of installation is disadvantageous from several standpoints. For example, the pump or blower is relatively expensive and creates potential safety problems due to the fact that it is electrically operated. Also, the output from the pump or blower is passed directly into the storage tank which pressurizes the tank and therefore increases vapor losses from the tank through its vent pipe.
Several recent developments have featured the use of an injector which establishes a reduced pressure zone in response to fluid flow from the storage tank to the vehicle receptacle, with the reduced pressure zone functioning to draw the vapors from the receptacle back to the tank. For example, in copending U.S. Pat. application Ser. No. 400,555, filed by Kirk Fowler and Elmer M. Deters on Sept. 25, 1973, and assigned to the same assignee as the present invention, and in copending U.S. Pat. application Ser. No. 534,448, filed by Trueman Hiller and Klaus Jarr on Dec. 19, 1974, and also assigned to the same assignee as the present invention, a gasoline dispensing and vapor recovery system is disclosed which incorporates such an injector.
Although both of these systems have considerably advanced the state of the art, they are incompatible with leak detector systems which are often incorporated in such installations. In particular, in the systems disclosed in the above applications, a portion of the flow from the main conduit extending from the storage tank to the vehicle receptacle is continuously diverted through the injector for establishing the reduced pressure zone before it is passed back to the storage tank. However, since the leak detector utilized in these type systems responds to pressure in the main conduit extending from the storage tank, the leak detector would be rendered inoperable since no such pressure is established by virtue of the continuous diversion of the flow.